Insights into the foaming properties of adzuki bean protein isolate as an alternative to egg white protein: Physicochemical and interfacial behaviors in foam decay mechanisms

Abstract

As the demand for egg white protein (EWP) alternatives grows due to concerns such as Salmonella contamination, avian influenza, and the increasing environmental awareness, plant-based proteins have gained attention as a promising solution. Compared to other legumes, adzuki beans are rich in sulfur-containing and hydrophobic aromatic amino acids, which may contribute to improved foaming properties. However, their functional potential remains largely unexplored. This study examined the foaming performance of adzuki bean protein isolate (API) relative to EWPs and soy protein isolate (SPI) under varying thermal and temporal conditions. API exhibited foam thickness and drainage comparable with those of EWPs and superior to SPI across 4°C, 25°C, and 83°C. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy revealed that API formed finer, more spherical foam structures with fewer ruptures, while SPI showed larger, unstable bubbles. Zeta potential and dual-fluorescent CLSM analysis indicated greater interfacial rearrangement in API, supported by its lower surface hydrophobicity and higher free sulfhydryl (–SH) content, which enhanced interfacial stiffness in rheology. Fourier-transform infrared spectroscopy analysis further revealed that API, like EWPs, showed increased β-sheet formation under heat, contributing to thermal foam stability, whereas SPI exhibited the opposite trend. In a meringue cookie application, API showed a lighter batter with greater air incorporation than SPI, highlighting its practical potential. Overall, this study offers new insight into the structural and interfacial mechanisms governing foam formation and decay, supporting API’s potential as a promising plant-based alternative for aerated food systems.